Substantial reserves of oil and gas have been discovered in the northern areas of Canada and Alaska. These discoveries have been made both offshore and onshore where the land is covered by tundra. Tundra provides vegetative insulation for permafrost which lies below the land surface of these latitudes. The passage of wheeled vehicles a number of times across the tundra over the same route can destroy the insulation for permafrost until such time as the fragile tundra can reestablish itself. The reestablishment process usually requires the passage of years. In the meantime, the permafrost can thaw and cause subsidence of the land until conditions are stabilized upon reestablishment of the tundra.
Because of these circumstances, and others, air cushion vehicles have been used to advantage in the northern portions of Alaska and Canada and have been proposed for use as support vehicles for oil and gas drilling rigs. Air cushion vehicles are particularly useful in these areas because they are relatively insensitive to the nature of the surface over which they are used. Air cushion vehicles can be used to advantage over the topography of the Alaskan and Canadian arctic, particularly ice, water, land, or marshy areas. An air cushion vehicle is attractive for arctic missions because, no matter how massive, its weight is supported by a cushion of air which does not significantly harm tundra and its vegetation.
Air cushion supported vehicles use a skirt structure to enclose a space between the vehicle body and the surface over which the vehicle is moved on hover. The lower portions of the skirt provide a slidable seal between the space and the surface, and this seal is established and maintained by air which is supplied to the enclosed space at superatmospheric pressure, normally 3/4 to 2 pounds per square inch above atmospheric pressure.
Various types of skirt designs exist for air cushion vehicles. A common type of air cushion vehicle skirt, and one which is widely used on air cushion vehicles in the Arctic, is that type of skirt known as the segmented skirt. In a segmented skirt, the overall skirt is defined by a plurality of pocket-like skirt segments which are mounted to a suitable support structure defined around the periphery of the vehicle hull, so that, when the several segments are properly mounted, they cooperate intimately with each other to provide the necessary enclosure to the hover space beneath the hull. The several segments are maintained in their desired configuration by hover air pressure which is supplied to them from a suitable source of pressurized air. This is typically a high-capacity, low-pressure blower carried aboard the vehicle which discharges to a suitable plenum structure via which hover air is supplied to the several skirt segments. Hover air can be supplied to the space enclosed by the skirt assembly via the skirt segments or both via the skirt segments and otherwise.
Where an air cushion vehicle is used over ice or land, a hazard exists that projections from the adjacent surface, such as a stump or sharp rock protruding from land or an ice pressure ridge protruding from an ice shelf, can damage the skirt structure. If the skirt is damaged, the efficacy of the skirt to establish and maintain the requisite seal around the enclosed spaces is diminished. A damaged skirt segment should be replaced as soon as possible before additional damage occurs to adjacent segments.
Present designs for segmented skirt assemblies for air cushion vehicles, while permitting replacement of damaged segments in the field, are also of such nature to require access to the damaged segment from the exterior of the vehicle. This is particularly disadvantageous where the need exists to replace a damaged skirt segment in an air cushion vehicle used in the Arctic. The extreme climatic conditions which prevail during the arctic winter may make it hazardous and inefficient for personnel to work outside the vehicle in order to accomplish skirt repairs.
It is therefore apparent that a need exists for equipment and procedures which enable repairs to be made to a damaged skirt segment from within the vehicle. The present invention is addressed to this need and provides equipment and procedures which enable the damaged skirt segment to be replaced completely from within the vehicle, rather than from outside the vehicle.